1. Technical Field
The present invention generally relates to location estimation technology using a combination of different positioning resources and, more particularly, to a location estimation apparatus and method using a combination of different positioning resources, which can estimate the location of a terminal based on a value obtained by combining the likelihoods of pieces of positioning information having different dimensions.
2. Description of the Related Art
Positioning technology using wireless communication infrastructure is present in various forms depending on the type of infrastructure and the range of service.
For example, a Global Navigation Satellite System (GNSS) denotes a system for determining the location of a user using signals of satellites in orbit around the Earth. As examples of this system, the U.S. Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS), European Galileo, etc. are currently operated or are expected to be operated. GNSS is deployed to service the entire area of the earth and is composed of a satellite unit for transmitting signals including precise time information and information about the orbits of satellites, a reception unit for receiving at least four satellite signals and calculating a location and a speed, and a ground control unit for monitoring and controlling the states and orbits of the satellites.
The GNSS provides high location accuracy and availability in which errors of 10 m or less occur on a plane or a suburban area in which direct lines of sight of the satellite unit and the reception unit are acquired. However, in a congested metropolitan area corresponding to a Non-Line of Sight (NLOS) area, there is a disadvantage in that a location error rises to 50 m due to multi-path errors, and, especially in indoor areas, it is impossible to determine a location and a speed because reception sensitivity is deteriorated and, consequently, signals cannot be acquired.
Further, “cellular-based positioning technology” refers to technology for determining the location of a user using the location information and measurement signals of a mobile communication base station. In detail, cellular-based positioning technology is classified into Cell-ID, Enhanced-Observed Time Difference (E-OTD), and Advanced-Forward Link Trilateration (AFLT) depending on the number of base stations from which a terminal is capable of receiving signals. Due to the characteristics of mobile communication infrastructure, having most urban and suburban areas as a service range, cellular-based positioning technology is advantageous in that the location may be determined even in indoor areas as well as in outdoor areas. However, it is difficult to apply such cellular-based positioning technology to indoor/outdoor navigation services which require a location accuracy of about several meters because the precision of positioning varies according to the density of deployment of base stations, and a relatively low location accuracy is realized, in which an average error of about 100 to 800 m occurs.
Furthermore, “Assisted GNSS” refers to technology for acquiring assistive information from a positioning server so as to improve the minimum reception signal sensitivity of a GNSS receiver contained in a user terminal device and shorten the initial location determination time (Time to First Fix). Assisted-GNSS enables fast location determination using a GNSS in a congested metropolitan area corresponding to a weak signal environment, but it is impossible to obtain a major improvement because signal strength is very low in indoor areas.
Furthermore, “Wi-Fi-based positioning technology” refers to a method for overcoming difficulties in indoor positioning, and may be representatively classified into a method for calculating the location of a terminal using the location and measurement signals of a Wi-Fi Access Point (AP) and a fingerprinting method using a radio map of the Wi-Fi AP. In this case, the method using the location and measurement signals of the Wi-Fi AP estimates the location of a target Wi-Fi AP using collection locations on a vehicle or a pedestrian at which signals are collected and received signal strengths (RSSI) of respective Wi-Fi APs, and calculates the location of a terminal by applying the estimated location of the target Wi-Fi AP to a positioning algorithm such as Trilateration, Weighted Centroid Localization (WCL), or Monte-Carlo. Further, the fingerprinting method generates a radio-map for a reference location by processing collection locations on a vehicle and a pedestrian and received signal strengths of respective Wi-Fi APs. Finally, the reference location having the minimum error in the received signal strength is estimated to be the location of the terminal by comparing the corresponding radio-map with the patterns of received signal strengths for respective Wi-Fi APs measured by the terminal.
When the results of analysis are aggregated, Wi-Fi-based positioning technology may provide precise location information of a terminal in an indoor environment compared to existing GNSS and cellular-based positioning technology. However, since the existing Wi-Fi-based positioning technology has difficulty in providing direction information (heading information) which is additional useful information in addition to the location information, it is not easy to filter abnormal location information. Further, in a walking environment using a terminal, a pedestrian moves more freely than when in an airplane or a vehicle, thus making it difficult to apply a formulated motion state equation to the walking environment.
Meanwhile, sensor-based positioning technology has technical features that mitigate the disadvantages of Wi-Fi-based positioning technology in an indoor environment. Basically, sensor-based positioning technology denotes technology for calculating the location of a terminal by combining one or more of an accelerometer, a gyroscope, a magnetometer, a barometer, an inclinometer, and a proximity sensor, which are provided inside or outside the terminal.
Such sensor-based positioning technology is advantageous in that that, first, it is almost completely uninfluenced by the external environment of the terminal, unlike GPS or Wi-Fi-based positioning technology. That is, since the location of the terminal is calculated using the internal physical features of a sensor (e.g. acceleration, velocity, rotational speed, etc.) as direct measurement information, there is a low probability that the corresponding measurement information will be distorted due to a complicated indoor environment. Second, even if positioning infrastructure is not present near the terminal, positioning of the terminal is always possible. That is, in the case of Wi-Fi-based positioning technology, positioning of the terminal is possible only in an environment in which a Wi-Fi AP is installed even in a given building, and thus it is impossible to perform positioning in an area in which a Wi-Fi AP is not installed. However, sensor-based positioning technology may always load sensor information and calculate the location of a terminal as long as a sensor is connected to the terminal, thus increasing the availability of the location information of the terminal. Third, recently, with the development of Micro Electro-Mechanical Systems (MEMS) technology and the popularization of smart phones, the price of sensors has greatly decreased. This phenomenon enables the mounting of sensors in smart phones to be further universalized, and thus combination with existing GPS technology is facilitated through such sensor mounting.
However, this sensor-based positioning technology also has problems to be solved. First, for sensors to which MEMS technology is applied, the quality of the sensors is not high. Thus, a calibration procedure for eliminating sensor error components occurring due to bias or drift must be essentially performed before the sensors are used. When this calibration procedure is not successfully performed, location error in a terminal, which is calculated using measurement information, greatly increases with the passage of time. Further, since error values attributable to bias or drift are different from each other in respective environments (e.g. temperature, etc.) in which the sensor or terminal is used, calibration must be able to be separately performed for each individual terminal that is used. Second, sensor-based positioning technology performs relative positioning rather than absolute positioning, and thus the absolute location of the terminal can be known only when the absolute location of a starting point (origin) is known. In order to overcome this disadvantage, combination with GPS, which is capable of providing an absolute location, is required. Third, sensor-based positioning technology may provide the precise location of the terminal for a long period of time only when accumulated location error is eliminated via a correction task that is performed during positioning, as well as a calibration task that is performed before positioning is started. The correction of the terminal is also implemented using location information from the GPS, which is capable of providing an absolute location, and Points of Interest (POI) in a map may be utilized for correction.
In connection with this, Korean Patent Application Publication No. 10-2015-0080817 discloses a technology related to “Apparatus and method for loading radio map database, and terminal device.”